The invention relates to a utility vehicle, in particular an agricultural tractor, with a steering system having single-wheel-suspended steering wheels, which are mounted on a respective wheel carrier, wherein each wheel carrier may be swivelled about the axis of at least one rigidly connected bolt which is connected via a ball-and-socket joint, to a transverse suspension element that is articulated to the vehicle body.
U.S. Pat. No. 5,538,274 describes a utility vehicle having a single-wheel suspension system for the steering wheels. The steering wheels are each mounted on a wheel carrier, which is connected via two ball-and-socket joints to an upper and a lower transverse suspension element. The transverse suspension elements are pivotally mounted on the vehicle frame and guide the wheel carrier during vertical movement of the suspension elements relative to the body vehicle. The ball-and-socket joints allow not only the suspension movement, but also the pivoting of the wheel carrier about an axle connecting the ball-and-socket joints, for the purpose of steering the vehicle. A ball-and-socket joint consists of a ball, which is rigidly connected to the wheel carrier via a bolt, and a ball shell that encompasses the ball and is an integrated component of the associated transverse suspension element. During pivoting of the wheel carrier, the ball is rotated within the ball shell in the same direction as the wheel carrier. During the suspension movement of the vehicle, on the other hand, the direction of motion of the ball extends perpendicularly thereto. These different directions of motion of the ball make precise detection of the steering angle, in proximity to the wheel, appear impossible. As precise detection of the steering angle is imperative for the automatic guiding of vehicles, for example by means of GPSs (Global Positioning Systems), the steering angle has in the past been detected indirectly on components of the steering device that are remote from the wheel. Thus, in the case of vehicles with hydraulic steering systems, in particular, the steering angle was determined by detecting the position of the piston in the steering cylinder of the steering device. However, as there is no fixed relation between the position of the piston and the position of the wheel carrier in steering devices of this type, the current steering angle has to be determined on the basis of the measured piston position using additional calculations. This entails considerable expenditure on hardware and software for the electronic equipment of the vehicle, particularly if a large number of vehicle types are equipped with different steering devices.
Although EP 0 888 951 B1 has disclosed a device for utility vehicles that allows the steering lock angle to be determined in proximity to the wheel, these vehicles are equipped not with a single-wheel suspension system for the steering wheels, but rather with a rigid axle. The wheel carriers of this rigid axle are connected to the axle body via simple axle bolts that form rotary joints and pivot with the wheel carriers. As the rotary joint is thus fixed to the axle body, the rotary joint merely absorbs swivel motions of the axle bolt that derive from a steering process and are detected by means of a suitable steering angle sensor that is attached to the axle body.
The object of the invention is to make in a simple manner a utility vehicle of the type mentioned at the outset suitable for automatic steering.